1. Field of the Invention
The present invention relates to an inspection apparatus, an inspection method, and the like which acquire information on a character and the like of a specimen using an electromagnetic wave. In particular, the present invention relates to an inspection apparatus, an inspection method, and the like which acquire information on an object character and the like using an electromagnetic wave in a frequency domain from a millimeter wave band to a terahertz band (30 GHz to 30 THz).
2. Related Background Art
Nondestructive sensing techniques using an electromagnetic wave in a frequency domain from a millimeter wave band to a terahertz band (30 GHz to 30 THz) (hereafter, it is simply called a terahertz (THz) wave) have been developed. Imaging using an electromagnetic wave in a frequency domain of a terahertz band has been developed, and has received attention as a safe see-through inspection apparatus which replaces X-rays. In addition, a spectroscopic technique which finds an absorption spectrum inside a substance and a complex dielectric constant using an electromagnetic wave which has a frequency domain in a terahertz band, and investigates physical properties, such as a bonding state, an analysis technique of a biomolecule, a technique of evaluating a carrier density and mobility, and the like have been developed.
The above-mentioned techniques are applied to defect/contamination inspections of moldings, component/contamination/defect inspections in chemical substances, and the like, and it is studied to use them for nondestructive quality checks in production lines of works. As their objects, in the case of chemical substances, ink, such as a pigment/dyestuff, toner, drugs, cosmetics, paints, and the like are conceivable. On the other hand, an inspection apparatus of drugs using a THz time domain spectrum analysis (Time domain Spectroscopy: TDS) method is proposed (Japanese Patent Application Laid-Open No. 2006-526774). This document expresses that an analysis of a type of internal drugs, and the like can be performed from a surface according to spectral information in a THz wave domain.
A conventional THz-TDS apparatus acquires data with scanning time delay between pump light and probe light. Therefore, typically, tens of seconds to several minutes are required so as to conduct a componential analysis in a 1-mm area. It is necessary to conduct an inspection in an actual factory production line at high speed. Therefore, a conventional THz-TDS apparatus cannot be applied to a total inspection in a factory production line.
On the other hand, the following technique has been studied in a coating inspection apparatus (Optics Communications, Volume 267, Issue 1.1 November 2006, Pages 128-136). The THz-TDS of the article widens a beam of a THz wave in a line, not in a spot, to acquire information on a large area simultaneously, and in consequence, acquires data from a two-dimensional domain at high speed. Furthermore, the THz-TDS acquires the terahertz wave two-dimensionally using an electrooptical crystal, and makes incident angles of the terahertz wave and an excitation light source differed on a surface of the electrooptical crystal to make delay time change locationally. In this way, the THz-TDS can acquire the information without scanning in a delay stage.
However, in a system using the above-mentioned linear beam, an electrooptical crystal which detects a terahertz wave two-dimensionally is indispensable. In that case, in order to compensate low conversion efficiency, a titanium sapphire laser is required as a large output excitation light source, and hence, the system becomes large-sized and expensive. In addition, although this system is to obtain spectral information in each point, inspection speed is not enough to use this system for a total inspection in a factory.
In the production line of a factory, there may be no large difference in an electromagnetic wave response every part of a finished product. When the line has been working over a long time in such a case, so long as it is possible to inspect fluctuations of an electromagnetic wave response in a certain amount of time, it is enough for operation and maintenance of the production line, or quality maintenance of finished products. For example, when pharmaceutical preparations of drugs are produced at high speed, so long as it is possible to acquire an average composition of the pharmaceutical preparations of tens to thousands tablets at high speed, it is possible to treat pharmaceutical preparations in a lot in which abnormality arises. It is also possible to feed it back to a production apparatus to return manufacturing conditions to a normal state in connection with it.